This invention relates to insulated solid propellant rocket motors. Specifically, this invention relates to an improved insulation/liner, or insuliner, for a solid propellant rocket motor.
The flame temperatures developed in the operation of solid propellant rockets often exceed 5000.degree. F. As the requirement for longer operation of solid propellant rocket engines becomes greater, the need for improved insulation materials to protect the case wall from the extremely high temperatures developed becomes more evident. The insulation must be able to withstand the high temperatures for periods of several minutes. In addition to the flame resistance, the insulation must also withstand erosion which is an action characteristic of combustion products. The primary objective of insulation is protection of the rocket motor casing. The amount of heat that can be tolerated by the motor case depends upon its material and structural design. In many applications, the case temperature must be kept below 300.degree. F. for the duration of the firing. Furthermore, in order to reduce the dead weight of a rocket, the insulation should have as low a density as possible, consistent with the flame and erosion resistance requirements.
A solid propellant grain must be securely fastened in a rocket motor case if problems are to be avoided when the rocket motor is fired. Even when the solid propellant grain appears to be securely bonded to the motor case, problems relating to separation and uncontrolled burning sometimes develop after ignition, and particularly in flight, where the forces caused by acceleration forces and other forces surpass the holding strength of the bonding material between the motor case and the propellant or the holding strength of bonding material between the propellant and liner material.
Currently, state-of-the-art rocket motor development involves a case-bond system which incorporates a liner, insulation, and special surface treatments, together with one or more primer and barrier applications to improve bonding, both to the case and to the propellant grain, and to prevent migration of ingredients out of or into the propellant. As a result, preparing the case-bond system is very complex and time-consuming, which translates into high cost and a strong possibility for poor reproducibility.
Recent advancements in the technology of bonding of composite systems, including propellant case-bond, have suggested the possibility of a single material which can function as both insulator and liner and which requires neither surface treatments to improve bonding nor primers or barriers to improve bonding and/or prevent ingredient migration out of or into the propellant. Such an insulating liner, or insuliner, would, at most, require only a thin coat of primer on the rocket motor case to enhance the insuliner-to-case bond.
One successful method of protecting the structural members of the rocket from hostile conditions was to provide a lining or coating containing asbestos. This type coating is adapted to withstand flame temperatures and the high velocity flow conditions resulting from the combustion of liquid or solid propellants. Such coatings or linings are capable of enduring for a time sufficient to allow complete combustion of the propellant. Asbestos-reinforced elastomeric insulation systems are the subject of Daly et al., U.S. Pat. No. 3,421,970 (Jan. 14, 1969), and Hartz et al., U.S. Pat. No. 3,347,047 (Oct. 17, 1967).
Environmental and health concerns led manufacturers to seek a replacement for asbestos-containing rocket motor case insulation which exhibits an acceptably low erosion rate. Junior et al., U.S. Pat. No. 4,492,779 (Jan. 8, 1985) disclose that a combination of powder filler and aramid polymer fibers may be substituted for asbestos in elastomeric compositions suitable for use as rocket motor case insulation, without loss of the high erosion resistance which characterizes asbestos-reinforced rocket motor case insulation.
Accordingly, it is an object of the present invention to provide insuliner compositions which satisfy the complex performance requirements for present and future solid rocket motors.
Other objects and advantages of the present invention will become apparent to those skilled in the art from a reading of the following disclosure of the invention.